1. Field of the Invention
The present invention relates to a method and an apparatus for heat processing of a substrate.
2. Description of the Related Art
In a photolithography process in the fabrication of a semiconductor device, various heat processings such as baking processing (prebaking) for vaporizing a solvent in a coating film after a resist solution is applied on the surface of a semiconductor wafer (hereinafter called “a wafer”) to form the coating film, baking processing (post-exposure baking) for promoting a chemical reaction of the coating film after a pattern is exposed, cooling processing after each baking processing, and the like are performed.
For example, in the aforesaid post-exposure baking processing, in order to activate an acid as a catalyst produced in the coating film by exposure, the temperature of the wafer is increased nonstop to a temperature between about 120° C. and about 160° C. so as to exceed a reaction temperature at which the acid is activated, for example, 80° C., and the wafer is baked at that temperature for a predetermined period of time.
Experimentation by the inventor, et al., however, reveals that when the temperature of the wafer is increased nonstop to the temperature between 120° C. and 160° C., the temperature within the surface of the wafer is made nonuniform in the early stage and not increased uniformly as shown in FIG. 9.
Accordingly, when the temperature is rapidly increased nonstop, the temperature of the wafer exceeds the reaction temperature while the temperature within the surface of the wafer is nonuniform, and hence the timings in which the temperature reaches the reaction temperature and the timings in which a reaction is started differ from portion to portion within the surface of the wafer. As a result, difference in reaction period occurs within the surface of the wafer, finally leading to the nonuniformity of the line width of a pattern formed on the wafer and a reduction in yield.